The overall goal of the proposed program is to develop an advanced electrochemical sensor for transcutaneous measurements of CO2 that is specifically applicable to neonates. The sensor will be accurate, reliable, safe, easy to use and designed to operate near normal body temperature. The specific aims of this Phase I program are to extend, through advanced sensor cell development, the patented Giner, Inc. electrochemical pCO2 sensor concept to transcutaneous (P(tc)CO2) measurement and demonstrate viable operation at 37 degrees C using in vitro and animal testing. The approach will be to test the advanced sensor configuration on newborn piglets to demonstrate concept feasibility and correlate P(tc)CO2 at 37 degrees C to arterial CO2 (p[a]CO2)measurements. There is significant potential for technological innovation. The proposed p(tc)CO2 sensor would have several advantages over current technology for neonatal application: 1) operation at 37 degrees C would eliminate burns that occur at 44 degrees C, 2) the signal is a direct function of pCO2 rather than a logarithmic pH response and will provide a more sensitive and reliable signal, and 3) the sensor will be more rugged (no glass) and invariant than the Severinghaus-type sensor. In Phase II an advanced prototype instrument with the unique P(tc)CO2 sensor cell will be developed and measurements will be extended to adults and, ultimately, neonates.